Advances in integrated circuit technology allow a single integrated circuit to perform functions that previously required multiple integrated circuits. As size parameters have decreased, semiconductor devices have gone through many iterations reducing the size of the semiconductor building block, the transistor. As little as ten years ago, transistor dimensions in the range of 3 to 5 microns were standard. Today, the semiconductor industry is attaining transistor dimensions of 0.5 to 0.7 microns. Paralleling the decrease in size of transistor dimension is the increase in the number of individual transistors that occupy a single semiconductor integrated circuit die. Ten years ago transistor densities in the range of 5,000 per die were possible. Today, chips containing 200,000 transistors per die are in production.
To use the many integrated circuits on a semiconductor die, the semiconductor die must communicate with the environment in which the packaged chip is used. One such environment is a circuit board, which may contain one or more packaged integrated circuit chips, and one or more discrete circuit elements, which are connected electrically. Semiconductor devices communicate by accepting electrical impulses supplied by an external circuit (as on a circuit board) connected to the chip, conducting those impulses to electrical circuits contained on the die, and reacting to those input impulses in a predetermined manner to generate electrical impulses that are then output from the chip to the external circuit (e.g., on the circuit board). The input and output of electrical impulses to the semiconductor chip occur over electrically conducting material, commonly referred to as leads. As transistor density has increased in each generation of semiconductor devices, so has the need to increase the number of leads available for connection to and from the semiconductor device. Nonsemiconductor integrated circuit devices, such as optical and superconductive devices, may also require high lead count packages.
Competing industry requirements of small semiconductor die size and large semiconductor lead counts has caused semiconductor manufacturers to develop new package devices. U.S. Pat. No. 4,800,419 discloses a support assembly that provides for closely spaced leads with fine definition. These leads are created on a tape-like structure using photolithography and/or etching processes. The semiconductor device package includes a flexible substrate having an upper patterned insulative layer, and a lower patterned metal layer including a multiplicity of package leads. An integrated circuit die is fixed to the upper surface of the flexible substrate. A rigid upper protective layer which partially encloses the integrated circuit and at least partially covers the top surface of the upper insulative layer is present. A lower flexible diaphram is attached next to the lower patterned metal layer opposite the rigid upper protective layer, and acts as a flexible wall to protect the lower patterned metal layer. In combination with the other elements, the lower flexible diaphram acts to enclose the integrated circuit die. The integrated circuit chip package has a multiplicity of electrical leads which provide electrical connections between the integrated circuit die and the package leads.
The packaging method of U.S. Pat. No. 4,800,419 maintains rigidity of the closely spaced, finely defined leads during the package assembly phase by providing an external support member around the perimeter of the package. However, afar the integrated circuit package assembly is complete the external support member is removed to allow installation into an external circuit. This leaves the rigid upper protective layer protecting the integrated circuit die, and the flexible diaphram providing support and protection for the lead assembly. It has been found that the lead assembly can be subject to injury. Delamination of the diaphram from the leads, and of the leads from the tape-like structure, can occur, as can lead deterioration in the form of cracking and separating. These problems are caused, for example, by moisture, or by flexing of the tape-like structure and diaphram supporting the package, especially during handling, transport or installation of the package.